The present invention relates to a method for broadcasting contents such as visual images and audio sounds, as well as to a receiver for receiving the contents broadcast by that method.
Contents such as visual images and audio sounds (i.e., net information excluding added data), to be telecast or transmitted by radio conventionally over such media as cables or radio waves, are broadcast and received simultaneously. In that setup, when to broadcast programs is determined solely by the transmitting side, and the media band width is monopolized by the contents being transmitted. If any contents are desired to be broadcast a plurality of times, the entire contents must be transmitted as many times.
If the contents are visual images that are digitally compressed, they still require a broad bandwidth for transmission. One way to ease the monopoly of the media by transmission of such huge data involves having digitally compressed and encrypted contents stored on a suitable storage medium (e.g., DVD) that may be distributed illustratively by mail while broadcasting only a decryption key for eventual decryption of the contents (as proposed by Japanese Published Unexamined Patent Application, publication No. 11-213553). The decryption key may be acquired by subscribers only.
The proposed way of distributing contents requires that users as subscribers receive both encrypted contents and a decryption key to decrypt the received contents. The users may play back the contents whenever they want and however they want it. Unlike conventional broadcasting, the contents in general are not reproduced by the receiving side at any specific time dictated by the broadcasting side.
To simultaneously broadcast and receive contents requires securing a broad band width for transmission, as mentioned above. Meanwhile, digitizing contents makes it possible for the distributing party to adopt, besides the above-described use of storage media, various rational means of distribution such as dividing the contents into a plurality of narrow band widths for transmission, and transmitting the contents on a narrow band width over an extended period of time. In such cases, simultaneity is lost. Still, the distributing party (i.e., the broadcaster) has numerous contents that the broadcaster wants to be received at predetermined times by the receiving side. Conventional techniques have so far been incapable of embracing such rational means of distributing contents while meeting the requirement for the contents to be viewed and/or heard in any intended time.
Where the same contents are to be broadcast a number of times, it may be desirable to transmit the contents only once before their repeated, predetermined playback so that they may utilize a broad band width as efficiently as possible. However, broadcasting arrangements offering these features have yet to be implemented by conventional techniques.